Can I measure CO2 also in a gas phase or only in liquid phase?

The carbon dioxide sensor was developed for measuring partial pressure of dissolved carbon dioxide in physiological solutions. Thus, the sensor membrane requires humidity for operation. However, under certain conditions it is also possible to measure CO2 in the gas phase. The CO2 sensor can be calibrated with CO2 containing gas mixtures of defined constant humidity for measuring CO2 in gas phase at the same humidity level thereafter. Changes in humidity will alter calibration.